There are now a vast number of technical devices, in which sensors monitor widely differing processes. In this case, objects which are like floating parts, for example dust, water droplets, smoke, also referred to in the following text as aerosols or else snow as well as gas bubbles, interfere with the monitoring processes in the detection area of the sensors.
By way of example in the case of an elevator, for example a passenger elevator in a building, the automatic elevator doors are normally monitored to determine whether an object is located in their movement path. If this is the case, the doors are not closed in order to ensure that no collision can occur, for example with a person. In normal conditions, this is undoubtedly a correct approach. However, in the event of a fire, serious problems can occur, since it is not possible to distinguish between smoke and an object. The following scenario may occur:                An elevator comes to rest at a floor where there is a fire. The door opens and the smoke enters the elevator cabin. People in the elevator wish to leave that floor again as quickly as possible. However, this is not possible because the door sensor identifies the smoke as an object and therefore a control system does not allow the elevator doors to be closed. People have already lost their lives in a situation such as this.        